Abstract
In this study, the all-optical control properties of photonic crystals based on self-assembled chiral-azobenzene-doped blue phase liquid crystals (CA-BPLCs) were investigated. The difference in the photothermal characteristics of CA-BPLCs with and without homogeneous surface alignment was discussed. Results revealed that surface alignment could induce more uniform and diverse blue phase (BP) structures, including BPII, BPI, and BPS-like phases during cooling. Consequently, the temperature range of BP was wider than that of the sample without surface alignment. All-optical control experiments with light illumination were then performed on the aligned or nonaligned CA-BPLC samples. During continuous irradiation with light beams at wavelengths of 405 and 450 nm, CA dopants underwent trans→cis and cis→trans back photoisomerizations, respectively. These processes promoted isothermal phase transition and wavelength shifting, which further enabled the all-optical control of the CA-BPLC samples. Various optical control modes of BPLC could be achieved through phase change and wavelength shifting by appropriately selecting the working temperature and surface treatment of BPLC. This study could be further used as a basis for developing photoswitchable and tunable BPLC photonic devices, such as light-controllable gratings, filters, mirrors, and lasers.
Highlights
Liquid crystals (LCs) have been widely applied to various fields, such as flat panel displays [1,2], electro-optical devices [3,4,5], biological [6,7] or environmental sensors [8,9], and topological defects [10,11] in a micrometer scale
The self-assembly 3D cubic structures of BPI and BPII are composed of orderly stacked double-twisted cylinders; cubic Blue phase LCs (BPLCs) can be regarded as photonic crystals (PhCs) that possess a unique photonic bandgap (PBG) and show colorful reflection characteristics [16]
Before the all-optical control capability of the chiral azobenzene (CA)-BPLC samples is studied, their basic optical properties should be understood in advance
Summary
Liquid crystals (LCs) have been widely applied to various fields, such as flat panel displays [1,2], electro-optical devices [3,4,5], biological [6,7] or environmental sensors [8,9], and topological defects [10,11] in a micrometer scale. Blue phase LCs (BPLCs) are among the most promising materials for advanced applications because of their superior characteristics, such as self-assembled three-dimensional (3D) photonic structure and fast response time [12,13,14,15]. Three different types of BPLC structures, namely BPIII, BPII, and BPI, can be observed when a chiral LC system is cooled from the isotropic phase. Crystals 2020, 10, 906 and BPI and BPII have cubic structures, corresponding to body-centered and simple cubic symmetries, respectively. The self-assembly 3D cubic structures of BPI and BPII are composed of orderly stacked double-twisted cylinders; cubic BPLCs can be regarded as photonic crystals (PhCs) that possess a unique photonic bandgap (PBG) and show colorful reflection characteristics [16]
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